A Conceptual Model for Puget Sound Sediments
The Puget Sound estuary is large, complex, and diverse
The Puget Sound estuary is a large, complex ecosystem spanning over 200 miles from Olympia, Washington north to the Canadian border and covering an area greater than 2,000 km².
This system was shaped over millennia by the movement of glaciers, resulting in the formation of many small and large bays, deep basins, and narrow passages.
Puget Sound has multiple geological features, distinct water bodies, and bottom sediments, resulting in a multitude of habitat types.
These Puget Sound habitats support unique and diverse communities. The habitats and their communities are influenced by many environmental and human-related drivers and pressures, as described in this story map.
Our Conceptual Model
The conceptual model depicted in this story map is based on the textual Driver-Pressure-State-Impact-Response (DPSIR) model (after Smeets and Wetering, 1999 ; Niemeijer and deGroot, 2008 ) that is presented in pages 9-11 of our program’s Quality Assurance Monitoring Plan .
Our DPSIR model describes the influence of environmental and human-related forces on Puget Sound’s many and varied ecosystem components, with a focus on the response of the sediments and their benthic invertebrate communities.
The model is described below.
Multiple drivers and pressures affect the Puget Sound watershed
The Puget Sound watershed extends from the snowcaps of the Northern Cascade mountains to the east and the Olympic mountains to the west, downstream to the estuary.
A multitude of forces, or drivers, affect the watershed. These drivers include inputs from the atmosphere, rivers, groundwater, and the Pacific Ocean, and from point-source and nonpoint-source waste streams related to human activity.
These drivers result in pressures associated with:
- carbon and nutrient loading
- chemical contaminant inputs
- climate change
Together, these pressures influence the state of Puget Sound’s pelagic (water column-related) and benthic (sediment-related) habitats, and ultimately impact the organisms that live in them. This includes the sediment-dwelling invertebrates, or benthos, studied by our team as part of the Puget Sound Sediment Monitoring Program .
Key questions
Guided by our DPSIR model, our team examines sediment quality and benthos throughout Puget Sound to assess the following:
- What is the condition of the benthic habitat, including sediments and their associated invertebrate assemblages?
- How does benthic condition change over time in response to inputs of carbon, nutrients, and chemicals to the system, and a changing climate?
Over time, we have been able to distinguish benthic communities with characteristics (impacts) that we consider to be either unaffected or adversely affected by regional and local drivers and pressures, and by the state of the local habitat. These two conditions are described below.
Scenario 1: Unaffected benthos
When ecosystem drivers and pressures are low, with:
- Low municipal, industrial, and agricultural activity
- Less development and human inhabitants
- Typical rainfall and temperature regimes
- Low nutrient runoff
- Low to no chemical contaminants
...and the state of the habitat includes:
- Water column conditions supportive of diverse and abundant pelagic communities that span multiple trophic levels
- Organic material processed throughout the water column, with limited amounts reaching the sediments
- Well-oxygenated waters and sediments
...we would expect to observe few impacts:
- Benthic communities unaffected by natural and human-related pressures. These communities are characterized by:
- high abundance and diversity measures
- both stress-sensitive and stress-tolerant taxa
Scenario 2: Adversely affected benthos
When ecosystem drivers and pressures are high, with:
- Higher municipal, industrial, and agricultural activity
- Dense development and human inhabitants
- Point-source and non-point source discharges of nutrients and toxic chemicals
- Altered rainfall and temperature regimes
…and the state of the habitat includes:
- Water column conditions that support pelagic communities with disproportionately low or high abundance, lower diversity, and altered trophic levels
- Excessive amounts of organic material reaching the sediments
- Waters and sediments that are poorly oxygenated, with increased levels of metabolic products such as hydrogen sulfide and ammonium
…we would expect impacts to include:
- Benthic communities adversely affected by natural and human-related pressures. These communities are characterized by:
- low or high abundance
- stress-tolerant taxa dominant
Visualizing benthic condition
With the complexity of this estuarine system, not every scenario can be depicted or discussed in this model. Despite these limitations, the model helps us visualize many drivers, pressures, states, and impacts that may influence Puget Sound sediments and benthos, and allows us to better create and test hypotheses about the status and trends of benthic condition.
This illustration is presented in our "The Scoop" on What We Do story map. Continue through the story map collection to learn more about Puget Sound sediment monitoring results.
